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OPTHALMOLOGY SURGICAL EMERGENCIES
Overview
The open environment in which the horse lives, their behavior, and the prominent position of the eyes predisposes the horse to injury to the eyes and surrounding bony and soft tissue structures. Ophthalmic (eye) emergencies in the horse can arise suddenly as a result of direct trauma, or they may be the result of a pre-existing non-traumatic condition that becomes suddenly worse. In all cases the goals of emergency treatment of ophthalmic disease are (1) to preserve the patient's vision, (2) to eliminate pain, and (3) to preserve as much as possible the cosmetic appearance of the eye. There are several common clinical signs associated with ophthalmic emergencies in horse.
Signs/Symptoms
Figure 1. Vertical orientation of eyelashes
Figure 2. Note filling of normal depression above left eye and the swollen eyelid
Figure 3. Clear discharge from the right eye
Cloudiness or discoloration of the cornea - This may be red, white, blue, or yellow discoloration of part or the entire usually transparent cornea (Figure 4, 5, and 6)
 
Figures 4 and 5. Affected eye appears blue
Figure 6. Tightly constricted pupil observed through a cloudy cornea
Change in contour (shape of the surface) of the cornea Obvious wound to the eyelids Presence of an obvious foreign body Presence of blood vessels extending from the periphery of the eye: this suggests a long standing problem that may have worsened suddenly (Figure 7)
Figure 7. Corneal blood vessels
When to Seek Veterinary Advice
Any change in the appearance of the eye or surrounding structures should be considered an emergency; owners or caretakers should seek veterinary assistance immediately.
Diagnostic Procedures
In order for the veterinarian to thoroughly assess the traumatized or diseased eye, adequate restraint in a stock is necessary. Horses that have pain associated with the eye typically require sedation and local or regional anesthesia (nerve blocks or anesthetic agents applied directly to the surface of the eye). Examination of the eye begins with a thorough gross examination, including palpation below the margins of the eyelids for the presence of a foreign body. The transparent surface of the eye (the cornea) and deeper structures of the eye, including the iris, lens and, if possible, the retina, are examined using an ophthalmoscope, lens, or slit lamp. Although the surface of the cornea may appear normal, damage to the most superficial layers can result in pain and predispose the eye to more serious complications such as infection. Therefore, all cases of ophthalmic trauma or disease should be assessed using special stains such as flourescein and Rose-Bengal. Normal cornea does not take up fluorescein stain and therefore does not fluoresce (turn green when examined with a special light). Damage to the surface layer of cells will result in a green fluorescence after the application of fluorescein dye (Figure 8 and 9).
 
Figure 8 and 9. Fluorescence following the application of fluorescein stain to the eye in a horse with a corneal ulcer
Rose-Bengal stain allows the veterinarian to evaluate the corneal tear film. This film is distributed over the corneal surface each time the eyelids close or blink. The tear film bathes the eye providing moisture to the surface and antimicrobial substance that are protective to the eye. Disruption of the corneal tear film predisposes the eye to serious complications, including infection with fungal organisms and drying of the surface of the eye.
In horses where a corneal ulcer is identified, a corneal scraping may be performed. This is a procedure where loose portions of the damaged cornea are removed. The collected material is submitted to the laboratory for cytologic examination (microscopic evaluation of the cells) and culture and sensitivity for bacteria and fungi.
If there is question regarding the bony structures of the orbit (eye socket) or deeper soft tissue structures, additional diagnostic imaging techniques such as radiology and ultrasound will assistant in the diagnosis of fractures, and abnormalities of the deeper structures of the globe.
Causes of Ophthalmologic Emergencies
1.) Orbital fractures
The orbit is a closed, bony cavity which contains the globe (the eyeball) and is filled with fat and connective tissue that cushion and protect the eye and its surrounding structures, such as muscles, blood vessels and nerves. The orbit is separated from the sinuses by a thin bony plate. Fractures may result in swelling of the eyelids, abnormal facial contour (shape), crepitus (air pockets that crackle when touched), epistaxis (nose bleed), and exophthalmus (bulging eye). Bone fragments can limit the eye's ability to move and impair its blood circulation. Orbital fractures may result in damage to other surrounding structure, such as the optic nerve (the nerve that provides vision) and cornea, resulting in corneal ulceration or blindness. Diagnosis is obtained by physical examination, radiography (x-rays; Figure 10) and ultrasound (Figure 11 and 12). Failure to repair large extensive fractures may result in permanent facial deformity (misshapen face, loss of normal function of the globe or eyelids, dry eye, and persistent or recurrent corneal ulceration and blindness. Treatment for fractures of the bony orbit include removal of loose or dead bone fragments and realignment of healthy bone fragments with suture, wires, or bone plates. Fractures of the bony orbit should be repaired quickly because fibrous (scar tissue) union of fracture fragments begins early, making repositioning difficult after several days. Routine wound care is performed for open fractures. Standard care for associated corneal wounds is outlined below.
Figure 10. Orbital and frontal bone fracture fragments and gas in the soft tissues in horse from Figures 1 and 2
Figure 11. Ultrasound appearance of displaced fracture fragments (arrows) seen in previous x-ray in Figure 10
Figure 12 Ultrasound appearance of a normal globe
2.) Eyelid lacerations (cuts)
Lacerations (cuts) of the upper eyelid are more severe than those involving the lower lid. Movement of the upper eyelid distributes the tear film that is responsible for preventing drying of the cornea. Flaps of skin hanging off the eyelid should never be removed, since there is almost always enough blood supply to produce a functional and cosmetic appearing repair.
Repair of the eyelid by stitching is usually performed in standing horses using sedation and local nerve blocks. The most important aspect of repair is to evenly align the eyelid margin. If the eyelid margin is uneven, tear film may not be distributed normally, resulting in corneal ulcers and damage from drying. Healing is typically rapid and sutures are removed after 10 days.
3.) Conditions Affecting the Cornea
The cornea is the outermost, transparent surface of the eye through which the pupil (the opening into the back of the eye) and colored iris can be seen. The cornea is transparent, has no direct blood supply, and has sensitive nerve endings. The cornea receives its nutrition from tear film. Diseases of the cornea are frequently recognized by owners because they result in pain and can cause changes in the transparency or color of the surface of the cornea.
One of the most common conditions to affect the cornea is corneal ulcers. The majority of these ulcers do not require surgical treatment. Uncomplicated corneal ulcers may heal as quickly as 7 days, even when untreated. Treatment usually consists of the application of topical antibiotics preparations and oral anti-inflammatories such as phenylbutazone or banamine. Topically applied atropine ointment or solution is commonly used to help dilate the pupil and relieve pain and intra-ocular pressure. With medical treatment, even horses with more complicated corneal ulcers usually improve after 24 hours. Horses that fail to improve rapidly or become worse should be reevaluated. Common complications of corneal ulceration that may require emergency surgery include keratomalacia (melting corneal ulcers), descemetocele (see below), and corneal perforation (penetrating wounds) and iris prolapse. Other conditions that may require surgical repair are corneal lacerations (tears) and corneal foreign bodies.
Melting corneal ulcers - Keratomalacia or a melting corneal ulcer (Figure 13) is the result of bacterial or fungal growth within the inner layers of the cornea after disruption of its outer surface. These organisms, as well as inflammatory cells in the corneal tear film, produce destructive enzymes that damage the inner corneal layers. Melting corneal ulcers appear blue-gray to tan or white and have a gelatinous or bubble-like appearance. They stain intensely with fluorescein stain and can progress to corneal perforation and rupture within a matter of hours. The eye is typically very painful.
Figure 13. Melting corneal ulcer
Descemetocele - A Descemetocele (Figure 15 and 16) is a corneal lesion that extends all the way to the thin inner lining (Descemet's membrane) of the cornea. Descemetoceles do not retain fluorescein dye whereas ulcers do. Descemetoceles can quickly rupture and therefore are considered surgical emergencies.
 
Figure 14 and 15. Two examples of a descemetocele. Note the clearing at the bottom of the corneal defect
Corneal perforation and iris prolapse - Corneal perforation (full thickness hole) may be the result of traumatic injury to the eye or progression of a melting corneal ulcer or rupture of a descemetocele. These require emergency surgical repair.
Iris prolapse: When a full thickness hole develops in the cornea, the colored iris can protrude through the defect in the cornea, filling the hole with tissue. (Figure 16 and 17).
 
Figure 16 and 17 Corneal perforation and iris prolapse
Corneal laceration (cuts or tears) - Corneal lacerations may be either non-perforating (extending only part way through) or perforating (full lthickness) and the result of either blunt or sharp trauma. Non-perforating, superficial corneal lacerations may heal completely with medical therapy alone. This includes topical antibiotic and antifungal medications, orally administered anti-inflammatory medications, topically applied serum or plasma, and topically applied atropine. Non-perforating corneal lacerations more than one-third the depth of the cornea or those that are irregular in shape should be treated with a combination of medical and surgical therapy. Perforating (full thickness) corneal lacerations are surgical emergencies.
Foreign bodies - Foreign bodies (Figure 18 and 19) in the eye can be found underneath the eyelids, on the surface of the cornea, under the third eyelid or within the eye itself. Most foreign bodies affect the cornea either by mechanical irritation, resulting in a painful corneal ulceration, or by varying depths of punctures to the cornea. The affect of the foreign material on the eye depends on the type of material (metal, plant material, etc), its location, and the size of the foreign material. Plant material is more commonly associated with complications because it can carry high numbers of potentially infectious bacterial and fungal contaminants.
 
Figure 18 and 19 Corneal foreign body (lead pellet)
Surgical Treatment
1.) Superficial Keratectomy - Keratectomy is a surgical technique used to remove partial thickness lesions from the cornea, such as foreign bodies or diseased tissue around corneal ulcers and to assist in the removal of corneal. Following removal of the abnormal cornea, the defect is routinely covered by a conjunctival graft (a flap of the white tissue surrounding the eye) to help seal the area and provide blood supply.
2.) Conjunctival Flap Graft - Conjunctival graft is a commonly used surgical procedure for the treatment of melting corneal ulcers, descemetocele, to cover a defect left following removal of a corneal foreign body (Figure 20) and as additional support for repaired corneal lacerations. They provide an immediate blood supply to damaged or abnormal cornea to speed healing and increase the amount of medications reaching the area. The graft will appear pink and rough but will gradually smooth out and shrink with time (Figure 21). A second surgery 6-8 weeks after graft placement may be required to detach the graft and help it shrink.
 
Figure 20 and 21. Examples of conjunctival grafts immediately after removal of a foreign body and 2 weeks after surgery.
3.) Corneal Laceration Repair - Tears or cuts in the cornea are close with very tiny stitches. Intensive medical therapy is required after surgery to improve healing.
4.) Corneal Foreign Bodies - Foreign material beneath the eyelids and third eyelid are typically removed surgically with the horse standing and sedated. General anesthesia may be required when the foreign bodies are lodged deep in the tissues.
5.) Enucleation (removal of the eye) -Enucleation or surgical removal of the eye may be necessary in cases of severe trauma or, when vision is lost, to quickly relieve pain associated with severe infection. The most common technique is to remove the globe (eyeball), place a silicon prosthesis (like a rubber ball) in side the socket to preserve the shape of the head, and then close the skin over it.
Medical Treatment
A variety of drugs can be used to treat horses with ophthalmic disease or injury.
Non-Steroidal Anti-Inflammatories (NSAIDs) - Usually administered orally. These include phenylbutazone (Bute), flunixin meglumine (Banamine) or aspirin. The primary reason these medications are administered is to reduce the signs of inflammation in the eye, especially pain.
Topical steroids - Topical or systemically administered steroids such as dexamethasone, prednisolone, or hydrocortisone should never be used in cases where the surface layer of cells of the cornea has been disrupted. These medications encourage development of severe fungal infections that may cause blindness or require enucleation.
Atropine - Spasm of the muscle that constrict the pupil are the primary reason for pain in inflamed eyes. Atropine relaxes these muscles and dilates (opens or widens) the pupil of the treated eye. Failure of the pupil to dilate following administration of atropine is an indication of severe inflammation that requires aggressive medical and possible surgical therapy. A potential complication to atropine usage is slowing of gastrointestinal motility, which can cause signs of colic. If dilation of the opposite untreated eye is observed (a sign of systemic absorption from the treated eye) or if the horse demonstrates even subtle abnormal GI signs such as being off feed, laying down more often than normal, or decreased fecal output, a veterinarian should be contacted at once.
Topical antibiotics - may be given as infrequently as 2 - 4 times per day in uncomplicated corneal ulcers or as often as every 2 hrs or even continuously through by an infusion pump in cases of severe corneal ulceration or in cases where melting or perforation is a concern.
Systemic antibiotics - These are used particularly in early cases of bacterial infection, corneal perforation, or if a conjunctival graft has been applied.
Topical and oral antifungal medication - Topical antifungal ointments may be administered to prevent fungal infections of the cornea. When infection or a melting corneal ulcer is already present, antifungal solutions are usually administered through a subpalpebral lavage system (a tube that runs under the eyelid) since the medications must be given frequently. Oral antifungal drugs are expensive and are probably not as effective.
Anti-collagenase - This is a group of topically applied or orally administered medications that counteract the affects of destructive enzymes that damage the cornea. These include serum or plasma collected from the patient, tetracycline, acetylcysteine, and orally administered doxycycline.
Subpalpebral lavage - Many horses with painful eye conditions do not tolerate frequent administration of ointments or solutions. In addition, horses have very strong muscles surrounding the eye and can tightly close their lids. The force needed to pry apart the eyelids for treatment can be great enough to rupture deep corneal ulcers or descemetoceles. Subpalpebral lavage (flushing) systems permit frequent administration of topical medications while significantly reducing the risk of complications. The system consists of tubing with a specialized foot-plate (Figure 22) that is passed through the upper eyelid and buried under the lid near the bony rim of the orbit (Figure 23). The tubing is secured with stitches to the skin above the eye (Figure 24) and then attached to the mane (Figure 25). Medication is injected into the tubing from the neck area and allowed to drip under the eyelid, either intermittently or continuously with a syringe pump.
Figure 22. Lavage tubing foot-plate
Figure 23. Insertion of lavage tubing through eyelid
 
Figure 24 and 25. Subpalpebral lavage system secured above the eye with suture and run through the mane to allow distant administration of medications
Prognosis
Prognosis for vision after an ophthalmic emergency depends on the type and severity of the injury and whether adequate treatment can be provided.
Fractures of the bony orbit carry a good prognosis for vision unless there is accompanying trauma to the cornea or globe. In these cases the prognosis is dependent on the condition of the eye itself. There may also be cosmetic defects if there has been depression of the fracture fragments or bone loss.
Eyelid lacerations without direct trauma to the cornea generally heal without complication, unless the repair fails to realign the lid margin properly. In this case failure of the eyelid to adequate distribute tear film can result in drying and recurrent cornel ulceration.
Bacterial and fungal ulcers have a favorable prognosis for retaining the eye and vision if they are recognized early and appropriate aggressive medical and surgical treatment is initiated. This includes control of the enzymes responsible for melting of the cornea.
Conjunctival grafts and deep corneal ulcers often leave corneal scarring, even with successful treatment. This however does not appear to affect vision in most horses. Horses in which corneal ulcers perforate have approximately a 40% chance of retaining the affected eye even with aggressive medical and surgical treatment. In many horse the globe will become blind and will shrink following rupture of a corneal ulcer, requiring removal of the eye (enucleation).
Although the prognosis for perforating corneal laceration is always guarded, those associated with blunt trauma generally have a poorer prognosis than those caused by sharp trauma. Blunt trauma causes more bleeding and inflammation within the eye, and horses with blunt trauma are more likely to have other damage to the inside or outside of the eye. Short corneal lacerations (less than 15-mm or 0.6 inches) have a better prognosis for vision with repair than longer tears or those extending beyond the junction of the transparent cornea and white colored sclera. Lacerations present for longer than two weeks or eyes that contain blood, infection, or other damaged tissues also have a poorer prognosis.
The prognosis for vision after foreign body removal is generally good as long as the material has not penetrated the full depth of the cornea or other external structures of the eye.
—Chuck McCauley, DVM
Diplomate ACVS
Posted 9/7/2006
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